HAWAII AGRICULTURAL EXPERIMENT STATION, .Q
Honolulu, Hawaii, October 25, 191e
SIn: I have the honor to submit herewith and to recommend for public
as Bulletin No. 45 of the Hawaii Agricultural Experiment Station a paper.. ...
titled "Potato Diseases in Hawaii and Their Control," by C. W. Carp ..l.....
pathologist of the station. The potential as well as actual importance of tim
potato industry in the Hawaiian Islands makes the present paper both-tinizely
and valuable. The absence of cold winter weather, together with the almo6.1it
continuous cultivation of patches to potatoes throughout the year in most m:ia i
tions, makes the problem of control of potato diseases much more difficult thiiAil
in the mainland of the United States. +i
Respectfully, '
J. M. WESTGATE, 1 ;.2
Agronomist in Charge-+,.^:i
Dr. A. C. TRUE,
Director States Relations Service, : ..|
U. S. Department of Agriculture, Washington, D. C.
.".::,": TMd
Publication recommended.
A. C. TRUE, Director.

Publication authorized.
D. F. HOUSTON,
Secretary of Agriculture. '.

HE,

I POTATO DISEASES IN HAWAII AND THEIR
I CONTROL.

CONTENTS.
Page. Page.
Introduction--------------------- 3 Potato diseases not known to occur
Prevention and control of potato in Hawaii--------------------- 36
pests------------------------ 4 Conclusion ---------------------- 41
Potato diseases known to occur in
Hawaii ----------------------- 15

INTRODUCTION.
The growing of Irish or white potatoes in Hawaii was at one time
a relatively important industry. According to Sedgwick,1 in the
middle of the last century potatoes stood at the head of the list of
exports and in 1849 the number of barrels exported was 51,957.
Since that time production has dwindled and consumption increased
until, in the year 1916, 189,212 bushels were imported from the coast
States, an amount approximately equal to former exports. Various
factors, not the least of which is the introduction of diseases, have
tended to make the growing of this crop difficult, while repeated crop
failures and discouraging marketing features are potent elements in
lessening production. The largely increased consumption has re-
sulted from the proportionate increase in the number of people using
this crop.
A considerable quantity of potatoes is still raised in the islands in
spite of the frequent crop failures. The greater part is grown in the
Kula and Makawao sections of Maui and near Waimea and Hama-
: kua, Hawaii. Small patches of from one-quarter to 5 acres are the
rule, and a considerable quantity is grown for home use. An ap-
proximation as to the present annual production is hard to reach,
though it is probably not in excess of 30,000 bushels.
;As a sound agricultural policy it is desirable that this languishing
S industry be fostered, and that so far as possible the Territory be
:: self-supporting with respect to this commodity. It is believed that
i by the application of improved cultural practices, fertilization, and
pest-control methods present production can be doubled or trebled
without any increase in acreage. The present rate of import of
this staple furnishes an indication of the available market.
Since the writer came to this station in 1916, attention has been
S largely devoted to a study of the potato crop and the reasons for
:.1:, Sedgwick, T. F. Potatoes. Hawaii Sta. Rpt. 1901, p. 374.

crop failures. It is estimated that from one cause or:`:::
least 50 per cent of the crop has been lost during the p6..; ^
observation. The experience of the past two years justified
elusion that potato-crop failures in the islands result frolm ..
lowing causes: (1) Use of poor seed, (2) continuous croppisg1%
diseases and insect pests, and (4) unsatisfactory soil conl".
Fundamentally diseases and insect pests are the most im'
factors, the others mentioned being merely contributing causes.
The diseases which have come under observation have beenV
fled, and the experience gained furnishes ground for the assu ...
that control measures found useful for combating these same..
eases in other sections are applicable here with but little -modifslw-'|
tion. It is realized that attention has not been -devoted toti
problem for a sufficiently long period to furnish a basis -for mlo
than tentative conclusions upon many of the problemso.'- : p............
production, but this bulletin has been written in order 'Wplt
results of the study into the nature of potato failures'fa.id:
measures into shape suitable for meeting the increasing m,
inform ation. ...... : c ...
Attention is directed to certain cultural practices in thbir reAtimn :..:
to disease, and the preventive and control measures which .huveb1b r giir
found applicable are described. Where no data are available farit3|
Hawaiian conditions, information as to methods -in use in. other. :::S:
localities is freely drawn upon. The diseases, insect pests, and othei::.....
causes of lessened yields thus far observed are discussed. .Several i
serious diseases affecting the Irish potato in other localities -but -o i:::3
yet found in the islands are described in order that Hawaiian potato '
growers may guard against their introduction.
PREVENTION AND CONTROL OF POTATO PESTS. I
GOOD SEED.
The question of what constitutes good seed is fundamental in the
growing of a healthy potato crop. Good seed potatoes should be ...
true to variety, from productive plants, firm, free from disease, ,:;-
uniform in size and shape, not overripe, and not weakened by sprout- i
ing. Such seed is difficult to obtain in Hawaii. It is probable thA :
satisfactory local seed can best be obtained by each grower's main-
taining a seed plat, or possibly a few growers in each section might .,
well specialize in seed production.
Certified seed.-The best seed is that from the mainland, certified "i2::.|:
by the authorities of the States. The label "Certified Seed" shows ::
that the seed has been grown under a system of State inspection.
According to the varying requirements of the different States suchn ]
seed is free from certain diseases and shows only a definite allowable ,'.
minimum of other specified diseases.,,1

POTATO DISEASES IN HAWAII.

The mere fact that the seed purchased is from the coast is not
sufficient indication of freedom from disease. Imported seed and
table stock used for seed purposes in the Territory are constantly
found infected with several serious diseases, among which are
Fusarium wilt, Rhizoctonia, black scurf, corky scab, etc. (See figs.
1 and 2.) Unless the seed is carefully inspected there is always the
possibility of introducing diseases not hitherto prevalent in the
islands. If mainland seed is used, the certified sort should be in-

sisted upon. Before planting it should be examined, sorted, if neces-
sary, and disinfected with one of the fungicidal solutions (p. 9).
The Fusarium wilt is a most serious disease almost constantly
carried by imported seed (P1. I) and very prevalent in California.
Probably the best source of seed for Hawaii is the Willamette
Valley, Oreg., where the Fusarium wilt is of infrequent occurrence.
The seed certification boards of some States allow a small percentage
of blackleg in stands passed as certified stock. It is necessary, there-
fore, to inspect carefully all imported seed for blackleg-infected
tubers (see fig. 7, p. 38) and to sort these out and destroy them.
The seed plat.-Ir, the chief potato sections a portion of the farm
should be set aside for growing seed potatoes for subsequent plant-

BULLETIN 45, HAWAII EXPERIMENT STATION

ings. Here the best available seed should be planted and pli ib
fully watched and cared for through the growing period. ..
Roguing.-Roguing the seed plat is practiced with the obj...
eliminating undesirable plants before the tubers are harvestwi
order that such plants may not be propagated. The plants airr...
amined from time to time and those not true to the variety or
diseased or otherwise undesirable are destroyed. Varietal ixtui|
can best be detected at flowering time. In roguing, a knowledVge:ij
potato diseases is valuable.
-0 .110 .: : .. ...EE::EE

4 4 .'.. t, .

t4

FIG. 2.-Potatoes that may be planted after treatment: A, Black scurf; B, common scabi. :|
Such potatoes may be planted after treatment, but it is better still to solect perfect j
types of seed tubers, like those illustrated by C and D, for planting. (From U. S. Dept. ;:;;
......

Seed from productive plants.-As many unproductive plants are j
found within a variety, selection should be practiced within the jj..
variety. Stuart1 has recorded the following results with 12 varieties, -:
showing the average yields from planting the progeny of strong and
weak plants:
Strong tuber units: 3.28 pounds of primes, 1.18 pounds of culls,
total 4.46 pounds.
Weak tuber units: 0.20 pound of primes, 0.51 pound of culls, total
0.71 pound.
1 Stuart, W. Good seed potatoes and how to produce them. U. S. Dept. Agr., Far ner' ::
Bul. 533 (1913), p. 7. A I
See irm rodctie lans.-Asman uprouciveithn~ant e :: : i!!i: ++[++'I,

POTATO DISEASES IN HAWAII.

r The strong plants gave more than 16 times as large a yield of
primes or merchantable tubers and only a little more than twice as
many culls as did the weak plants.
Hi Uniformity.-Selection has shown that within a variety there are
Strains which, when isolated, behave in a more or less uniform manner
I with respect to size and shape of tubers. Selection should be prac-
S ticed from the hills at the time of digging the seed plat, keeping as
specially desirable seed, tubers from hills yielding a maximum num-
ber of healthy tubers of fair size and uniform shape.
Hill selection.-This method of selecting seed consists in marking,
by stake or otherwise, the most desirable plants during the growing
season. At digging time those marked plants having a maximum
number of desirable tubers are specially set aside for seed. In this
way desirable varietal characters of the plants and high-yielding
qualities are selected together.
Immature seed.-European growers have come to believe that, other
things being equal, larger crops are produced by immature seed than
by mature seed. This refers to maturing of the seed in the ground.
Most of the locally grown seed at present is immature, since the fields
are regularly visited by blight or the tops dry up with the Fusarium
wilt disease, etc., at about the time of flowering.
Large i'. small seed tubers.-The use of small seed tubers can be
countenanced only when these are known to be the progeny of
productive plants. From the quotation from Stuart (p. 6) regarding
the yield of strong and weak plants it will be seen that the strong
plants produced more than 16 times as great a weight of large tubers
as the weak plants, but only a little more than twice as great a weight
of small tubes. In selecting small tubers from the lot it is evident
that a large proportion of tubers from unproductive plants would
be chosen.
Ballou I writes as follows regarding the use of large and small
tubers for seed:
[The use of large tubers gives] : (a) A very heavy, perhaps almost total,
percentage of the high-yielding strains; (b) a heavy percentage of the average
or moderate-yielding strains; (c) a very small percentage of the inferior or
low-yielding strains.
[The use of small tubers gives]: (a) A very insignificant percentage of
the superior or high-yielding strains; (b) a small percentage of the moderate-
yielding strains; (c) a very heavy, almost total, percentage of the low-yielding
or inferior strains.
The significance of the above data with respect to the common local
practice of marketing all fair-sized tubers and keeping only the culls
for seed needs no comment.
SBallou, F. H. The status of the potato-growing industry in Ohio. Ohio Sta. Bul. 218
(1910), p. 587.

BULLETIN 45, HAWAII EXPERIMENT STATIOl.

Whole v. cut seed.-Provided the young plant is furnished wl--:
ha
sufficient supply of nourishment by the seed piece until able to.....i)j
orate its own food, there does not appear to be any difference whoA
the seed be entire tubers or cut pieces. It is true, however, that. 'ir
limits the larger the seed piece the larger will be the resultant o..:00 f
but the smaller the percentage of marketable tubers. Whole tu Ib ..
insure a good stand with greater freedom from disease. Howe:ver|l,..
the growth of too many sprouts is to be discouraged, since too g iat ..
a number of tubers will be set and comparatively few will be abl
reach a satisfactory size. ....
Greening the seed by exposure to light.-In order to hasten the-"
germination or sprouting of seed, that is, to shorten the rest period,
it is a common practice in Kula, Maui, to spread the tubers to be.
used as seed, as soon as they are dug, under a thin shade of bushesi
for several weeks or until they sprout. It is claimed that they will:::
sprout in about half the ordinary dormant period. There is as y
no experimental evidence to support or controvert this statement O $:
the farmers. This exposure, especially to the high temperature 'of :
midday, probably serves to prevent any tendency of the seed to rot
from the late blight fungus, but results in loss from other rots and 9
from such insects as the tuber moth. The shortened period of dor- ..
mancy, if a fact, is advantageous when potatoes are grown almost |
continuously and seed is difficult to obtain at certain seasons.
Seed selection in relation to disease control.-Seed selection is not '
only of value in obtaining pure high-yielding strains within a va-: .. ...,...
riety, but it is of fundamental importance in preventing those diseases .
which are carried by the seed. Such supposedly nonparasitic but
inherent diseases as curly dwarf, leaf roll, etc.; the fungus diseases .l
late blight, Fusarium wilt, rosette (Rhizoctonia), and those due to
the scab fungi; as well as certain insect pests, are carried by the seed. !
For avoiding these diseases any of the following well-known methods ',
of selection are available: (1) Selection from the pile or lot, (2) field
selection, (3) hill selection, and (4) regional selection and use of cer- .
tified seed. ..::||...
Selection of healthy tubers of uniform size and shape for seed from H
the mass is valuable in disease control, though not necessarily so
in obtaining productive strains. As mentioned above, hill selection
is of value both in disease control and in obtaining productive strains. ;
Regional selection and the use of certified seed may well serve as
means of starting seed plats in Hawaii. Seed should not be obtained ;
from regions or from fields where noxious pests are known to be
prevalent.
Cutting seed.-In cutting potatoes for seed the tubers must be so
cut that each seed piece or set shall have at least one strong eye, and
it is desirable that each shall weigh about 1 ounces. First cut a .
thin slice from the stem enid of the tuber and examine the flesh for *

POTATO DISEASES IN HAWAII.

Discoloration of the vascular or woody ring. Brownish or black
Discoloration at this point indicates Fusarium wilt or other infection.
Such tubers are not suitable for seed. Then cut the tuber length-
wise through the bud cluster at the end and through to the stem end.
Then divide each half crosswise. With large tubers further division
can be made, but the cuts should always be so made as to insure
blocky pieces when possible. It requires about 22 bushels of seed
adequately to plant an acre at the standard distance of rows 3 feet
apart and seed pieces 1 foot apart in the row. Less than half this
Amount is commonly planted.
Potato seed disinfection.-Diseases such as corky scab, Rhizoctonia
scab, and rosette (P1. VIII), which are carried on the surface of
,' the seed, can be controlled in some degree by soaking the seed in
i a disinfecting solution. Seed disinfection will be of little value if
the soil is already infected with the disease for which the seed is
treated. It is on the whole a better practice not to cut the tubers
before soaking them in the disinfecting solution. For immediate
planting, however, the tubers may be cut before dipping.
SThe solutions most frequently employed for potato disinfection
are formalin and corrosive sublimate. Either is suitable for the
corky scab, but the evidence is in favor of the latter solution for
the Rhizoctonia diseases (black scurf and rosette).
The usual formalin solution is made up as follows:
Formalin (40 per cent formaldehyde)---------------pint- 1
Water to make-- -- -------------------- gallons- 30
The sacks containing the potatoes should be immersed in this
solution for two hours, after which the tubers should be removed
and spread to dry. Thirty gallons of the solution is sufficient for
disinfecting about 30 bushels of seed.
Corrosive sublimate has the disadvantage of being a deadly inter-
Snal poison, and it should be handled with this fact always in mind.
The solution corrodes metal and therefore only wood and nonmetal-
lic containers should be used. The formula is as follows:
S..Corrosive sublimate__ --- ---------------------ounces-_ 4
SWater ----------------------------------gallons-_ 30
: Dissolve the chemical in a few gallons of hot water and dilute to
30 gallons. Immerse the sacks containing the tubers for two hours,
then remove and spread the potatoes to dry. As this solution loses
its strength after treating four to six lots of potatoes, fresh solution
should be substituted.
SUITABLE POTATO SOIL.
Kind of soil and method of treatmernt.-So far as possible soil
free from potato diseases should be chosen. As the Irish potato is
a cool-climate crop, in the Hawaiian Islands it is at home at an ele-

10 BULLETIN 45, HAWAII EXPERIMENT STATIONT.:-Il
ovation of 2,000 to 3,000 feet or more on rather loose-tetu.i.!!
drained soils. In any case heavy wet soils poorly drain4:: a.....
to work are not suitable for potato culture. In some pottsB
Kula, Maui, the presence of a layer of hardpan a few iA4S
the surface indicates that shallow surface plowing has too :h
practiced and that the conditions of apparent soil exhaus :io:i
be largely improved in such fields by deeper plowing. HUD-
the plants might well receive more attention as an aid in
attack by the potato tuber moth. Crop rotation should be
ticed more and more here, not only to increase the fertility otlf: ....
soil but also to combat the prevalent diseases and insect pests.
selection is almost useless or is of temporary value unless co
with rotation. The organisms causing Fusarium wilt, rosette, h1....
scurf, corky scab, etc., live indefinitely in the soil, but it is
believed that in the absence of susceptible plants the virility 4y-
organism is lessened and the number decreased. Similarly,
tuber moth, which is most serious in dry years, can possibly be
under control by clean cultivation and rotation combined wkkitM:
telligent spraying with arsenicals. Crop rotation, combined -iviii\
the use of good seed and preventive sprays, offers promising oppod:ii.
tunities of improving the Hawaiian potato industry through ini.:
creased yields and better quality.
Soil reaction.-As certain organisms are favored by an acid siA:.lj
while others are encouraged by an alkaline soil, the latter beilg
favorable to the development of corky scab, lime or wood a" .i
should never be applied to potato fields, as they tend to produeeii..
alkaline soil reaction and are sure to encourage scab. On the oth.p.:
hand, the plowing under of green-manure crops will tend to miM..
the soil acid and thus reduce the damage from this disease. TboIm
Rhizoctonia diseases are thought to. be worse on heavy, poory'
drained, acid soils. Correcting the drainage and aeration of su4"::;.
soils is beneficial. ',
SPRAYING. SPRAY MIXTURES, BAITS. ETC. ;
In order to protect the potato plant against various insect pests aM;
fungus diseases, sundry chemicals are sprayed or dusted thereon or.: .
used as baits. The chemical used varies with the nature of the pest-'
there are no cure-alls. The material may serve as a protection of 'thwHiii
foliage against fungus infection or as a contact or internal poison fori
insect pests. In certain weather conditions, a coating of spray m#.
act mechanically to prevent sun injury of the foliage. 'M
Bordeaux mixture for the control of foliage diseases.-The mS,
widely used fungicidal spray for the prevention of foliage disease mof
the potato is Bordeaux mixture. The experiments carried on wiky
this spray by the writer alone and cooperatively with others i,::

I POTATO DISEASES IN HAWAII. 11

Hs!awaii for the prevention of the late blight disease have been very
ncouraging. The fact that late blight is present upon almost every
to crop grown, and that when it is too dry for this disease the
0arly blight is serious, should be sufficient argument in favor of uni-
versal spraying of potatoes with Bordeaux.
SStandard Bordeaux mixture is made up according to the following
Formula, which is often referred to as 1 : 1 : 10 or 5:5:50 Bordeaux.
Bluestone (copper sulphate)---------------------- pound-- 1
Quicklime (not air slaked)---------------------------do-- 1
Water to make---------------------------------gallons-- 10
The mixture is prepared by dissolving the bluestone by hanging it,
preferably overnight, in a sack immersed, the top just under the sur-
face, in a gallon of water in a wooden container. If time is a factor,
pulverize the bluestone and dissolve it in a gallon of hot water.
Dilute to 5 gallons. Make a lime paste by slaking the pound of lime
in a small quantity of water, adding enough water to prevent its boil-
ing dry. When the boiling ceases, stir to a smooth cream and add
water to make 5 gallons. Just before the Bordeaux mixture is re-
quired for use, pour the 5 gallons of diluted bluestone and 5 gallons
of diluted lime at the same time into a wooden container and stir
vigorously. Stir and strain into the spray tank and agitate occa-
sionally while spraying, as even properly made Bordeaux settles
gradually. The bluestone solution and the lime solution can be kept,
but Bordeaux mixture should be used the day it is made. However,
if sugar is stirred in at the rate of pound to 10 gallons the day
the mixture is made, Bordeaux may be kept several days in covered
wood containers.
Where considerable spraying is to be done, it is advantageous to
prepare stock solutions of the bluestone and of the lime. It is con-
venient to prepare these solutions so that each gallon contains a
pound of chemical. Then to make 50 gallons of Bordeaux, it is neces-
sary only to take 5 gallons of the bluestone stock solution and dilute
it to 25 gallons, to dilute similarly 5 gallons of the lime stock solu-
tion, and to mix the two diluted solutions.
2 It is as easy to prepare Bordeaux mixture by the right method as
by any other, and properly made Bordeaux is much more effective
Than the mixtures of uncertain physical and chemical composition
which result from haphazard methods. For the most effective Bor-
deaux it is essential that the bluestone solution and the lime suspen-
sion be diluted before combining. When properly made and properly
applied, Bordeaux has remarkable adhesive properties, once it be-
comes dry on foliage.
The active principle of Bordeaux mixture is the copper, but in
order not to injure the foliage and to render the treatment more last-

12 BULLETIN 45, HAWAII EXPERIMENT STATION. -"
'* ": -""ig l^
ing the copper is made insoluble by the use of lime. When'-.
luted solutions come together minute precipitation membraa'
formed. In spraying, the plant is covered with a thin layer i
minute membranes. The copper in the membranes, rendered:.-.:l
soluble by the action of the carbon dioxid of the air, forms..A
tion in any minute films and droplets of water on the leaves,j
prevents the germination of fungus spores. :
The Bordeaux should be applied on both upper and lower i
faces of the leaves and at the highest pressure obtainable to I
thorough protection and economic distribution. Each plant sh""l|
be sprayed long enough to cover all parts but not sufficiently
to allow the sprayt;
collect in drops
runoff, as inthel
case the spray i.s
^ 6 only wasted but is leq
I aadhesive. The planil.
will hardly show tjy.
N ... .
spray when it A.P
b e e n properly an4i
thoroughly a ppli4.,t
.^ jnsr i/with sufficient pr
sure and in the desir
v^ aable misty form. (Se|::.:`
fig. 3.). .:.,, ,ii
Perhaps under Ha.,
u waiian conditionsjl
(^ /\some variations of te :t:he
U formula for Bordeaux -
FIG. 3.-Desirable types of hand sprayers, with extension as given may be found 3
rods permitting thorough underspraying of the foliage, advisable. Possibly .
pounds of bluestone and 4 pounds of lime in 50 gallons of the mix*-:
ture would do the work satisfactorily. ,.
Where there is difficulty in spraying plants due to the waxy suiii
face of the leaves, or where the spray does not stay on owing to heavyl
rains, a sticker made up according to the following formula may be i
used to advantage:
Resin ___--------------------------------------------- pound- 1 '
Sal soda (crystals)----------------------------------do-- ,
Water --------------------------------------------gallon__ ..A
The ingredients should be boiled together until a clear browiw
sirupy liquid appears, then cooled and added to 50 gallons o.:..i
Bordeaux mixture (or proportionately for smaller quantities of
spray). ,'

POTATO DISEASES IN HAWAII.

Modifications of Bordeaux mixture for the control of leaf-eating
1inuuects.-For controlling leaf-eating insects, such as the army worm
I wor "poko," and as a possible aid in combating the tuber moth, Paris
green may be used in Bordeaux at the rate of 1 pound to 50 gallons.
SUsually Bordeaux mixture contains a sufficient excess of lime to
I neutralize the Paris green and no burning of the foliage results,
Sbut if lime of doubtful quality is used in preparing the Bordeaux,
7 an amount of lime equal in weight to the Paris green should be added
to prevent burning.
The usual method of destroying leaf-cutting insects (fig. 5, p. 31),
however, is by adding arsenate of lead to Bordeaux mixture at the rate
of about 3 pounds to 50 gallons. Whether this form of poisoning
will prove more satisfactory for the leaf-eating cutworms or" pokos"
than the locally commonly used flour-Paris-green-dust bait remains
to be seen. For the tuber moth, arsenate of lead in Bordeaux will
probably be of considerable benefit.
Lime-sulphur spray or dry sulphur for the control of mites.-For
P the control of the potato mite (Pls. XII and XIII), which in dry
and hot situations causes the death of young growth and premature
development of the plant, a lime-sulphur spray made up as follows
has been found effective:
Sulphur -----------------------------------------pound-- 1
Quicklime ----------------------------------------do--- 1
Water to make--------------------------------- gallons-_ 20
Boil the sulphur and quicklime in a gallon of water in a kettle
or pan until they combine into a yellowish sirupy liquid, this usually
requiring about three-quarters "of an hour. Dilute to make 20 gal-
lons of spray mixture.
Dry surphur dusted upon the foliage with an insect-powder blower
is likewise effective in the control of mites.
Boil fungicides for Sclerotium. wilt.-Ammoniacal copper carbon-
ate solution and "eau celeste," which contain copper in soluble form,
are recommended as soil fungicides in case of Sclerotium wilt
(p. 26). The chemicals needed to make sufficient solution for 50
gallons of copper carbonate fungicide are as follows:
Copper carbonate------------------------------- ounces-_ 5
Ammonia (26 Baume)--------------------------- pints-- 3
Water to make-------------------------------- gallons- 50
To a gallon of water in a wooden vessel add the ammonia and stir.
Add the copper carbonate a little at a time, stirring constantly. Con-
tinue to add the chemical until no more will dissolve. Allow any
undissolved carbonate to settle to the bottom and draw off the clear
blue supernatant liquid. This solution does not keep well for more

13

14 BULLETIN 45, HAWAII EXPERIMENT STATION. '"
.... ..::: ..:::'! ::i... 'i
than a few days, and is best prepared fresh as needed..-f.lm
dilute the solution to 50 gallons.
Since bluestone may be more readily obtained than copper I
bonate, the formula for another soil fungicide, eau celeste, is giv.
Bluestone (copper sulphate) ---------------------pounda_ 2' :
Ammonia -----------------------------------pints-.
Water to make--------- ------------------ gallons-- 50
Dissolve the bluestone in a gallon of water. When dissolved,-:
the ammonia to it. Transfer to bottles that can be tightly cortL" ;
the solution is not to be used at once. For use dilute to 50 gallor30.II
A half-teacupful of either of these solutions sprayed in time at h
base of each plant is said to protect the plant against Sclerotium wlt'!!!
Poison baits for army worms.-Where an invasion of army woeiri0
comes from adjacent grassland, cultivated fields may be prdtedei4
by surrounding with a line of poison bait or establishing such a ii
along the threatened side. Ditches sprinkled with lime serve tW'.
same purpose. -"* -
Paris-green bran mash as bait for cautworms.-With 25 pounds !i|
bran thoroughly mix while dry pound Paris green. To make the,
bait attractive chop fine six lemons or waste citrus product, papaya,
etc., and add to the mixture, or add a quart of cheap molasses. -
Thoroughly mix and add sufficient water to moisten the mixture, but .
not enough to make it sloppy and thus interfere with its easy and
economical distribution.
Arsenate of lead may be substituted for the Paris green, using
four to six times as much, or of white arsenic half as much as ofI
Paris green may be used.
Criddle mixture for cutworms.-The following formula is largely
quoted as an effective bait for cutworms. As a cheap substitute for
cereal baits it is well worth trying.
Fresh horse dung---------------------------pounds- 60 ::
Salt ---------------------------------------do--. 2
Paris green----------------------------- -pound_- 1 ..
The Paris green is mixed with enough water to form a thin paste.:::
and it is then thoroughly mixed with the horse dung. "

HANDLING, SORTING, GRADING, AND STORING. :

To prevent bruising, potatoes should be carefully handled at alli.I
times. The slightest wound is sufficient to open the way for *the .I':
entrance of rot-producing organisms. Care in handling is especially|
necessary at digging time when the skins are tender. '
All bruised and rotted tubers should be sorted out before shipping.:ii
or storing, and if the crop is to be stored any length of time re-s rting :::'1

.-i
t
... "E..::'n

POTATO DISEASES IN HAWAII.

imay be necessary. Potatoes carefully graded as to size are much
"pr readily sold at a good price than when large and small are
.. All potatoes of inferior size should be sorted out and used
E.the farm. It is a poor policy to leave in the shipment any bruised
r decaying tubers, as these are valueless and by wetting and other-
wise making the lot unattractive they may result in considerable loss
to the shipper through market charges for re-sorting.
Outside the cold-storage warehouses a sufficiently cold place for
the storage of potatoes is difficult to maintain in Hawaii. For the
Best results a temperature of about 35 F. is required. It is probable
that houses quite suitable for the storage of this crop could be con-
Sstructed at the higher altitudes where potatoes are most successfully
Grown should there develop sufficient economic advantage in holding
Sthe crop. Since the potato consumption in the islands is so greatly in
excess of the production, there is little incentive to store. However, a
Small storage place, screened against insects, tightly built, and pro-
vided with close-fitting doors, so as to take advantage of the night
temperature, would be valuable in preventing loss from shipping to
a glutted market. The place could be used for holding seed stock,
Sfor fumigating and storing beans, corn. etc.

POTATO DISEASES KNOWN TO OCCUR IN HAWAII.
CLASSIFICATION.
In order that plant diseases may be intelligently combated, an
understanding of their nature is necessary. According to their
causes the diseases to which the potato is subject may be divided into
Stwo classes: (1) Those caused by organisms, as fungi, bacteria, in-
sects, etc., which may be called parasitic diseases; (2) those induced
by unfavorable growing conditions or by obscure and undetermined
causes, which may be termed nonparasitic diseases.
The parasitic organisms which cause diseases of the first group
may be present in the soil, introduced on the seed, or brought to the
soil and the growing crop from adjacent fields by wind or water.,
SUnder favoring conditions in the presence of the potato plant, the
0. disease progresses more or less virulently. The following parasitic
J diseases, grouped according to the nature of the parasite as fungus
Lor insect, have been found factors in potato production in Hawaii:
Fungus diseases, including Fusarium wilt (Fusarium oxysporum),
late blight (Phytophthora infestans), black scurf and rosette (Rhik-
oetonia so8ani), early blight (Alternaria solani), common or corkv
scab (Actiomyces ckromogenus), tuber rots (Fusarium oXysporum,
F. radiccola, and F. coeruleuwm); insect pests, including tuber moth
(Phthorimaea operculella), cutworms and a similar leaf-eating worm

15

The nonparasftic- diseases of the potato may be oxsio
favorable environment such as unsatisfactory soil-,..
even growth due to prevailing weather conditions, or.
chemical injury from.* injudicious applications of arseni::i'aU
Bright, hot sunlight after certain kinds of weather fre ..quen
sunscald and tipburn of the leaves. It may be noted tha|:.....
the diseases usually classed as nonparasitic, though imnperfe|"B
derstood, can be controlled through seed selection and elimint
undesirable strains. Such are the inherited diseases, leaf roll,
dwarf, and mosaic, which probably will not be serious faqWtorsl WI
Hawaiian potato industry. ..,
*-'o*--*r-t-.iia
IDENTIFICATION. ...'
Many times a knowledge on the part of the grower of the d.f..
diseases which attack the potato would save crops now ned:-
lost through failure at the critical time to apply the proper treat
to hold the disease in check.
Plants which appear unhealthy for any reason should be exenil
with the following points in mind; and with the accompanyiwot
as a guide, a working knowledge of epidemic diseases in Hawaiiw.
soon acquired. All growers should learn at least to recognize 1;
blight, early blight, mite disease, Fusarium wilt, and rosette. ,J
POINTS TO BE NOTED IN EXAMINING A PLANT. .
Note how the ,plant differs from the normal. If the leavesW
diseased spots, note their character. If the leaves wilt, note l
ones do so, the new small leaves or the lower older leaves,. -1
presence of worms in the leaves and stems indicates tuber mM
If the new top growth curls, twists, becomes fuzzy, and dru i
while at the same time the leaves become bronzed on the lotetlS
it is the work of the potato mite. If the lower leaves wilt and di
off more than normally or some leaves roll up in tubular forms
no diseased spots are present, examine the underground stemi e
the soil level. If it is girdled with a cankerous, dry, brown lui
Rhizoctonia may be present, causing rosette disease, or if -the :.A
is here a shell with the center rotted out, the plant is perhaps13
tacked by Sclerotium wilt. Sometimes the stem borer does sinl
damage, in which case the burrow is readily traced and the w1o
found. If the stem appears normal externally, split it wiTi
knife and examine the inside at the ground level and below;ll.
the vascular tissue-that is, the woody portion a short distaw4iA
from the surface-shows a'brown discoloration which is tra|
toward the root system, the plant is suffering from lack of
because its water-conducting apparatus is plugged by fungus tfa
(Fusarium wilt). i

FIG. I.-CUT STEM END OF TUBERS SHOWING DISCOLORED
VASCULAR RING.

FIG. 2.-STEMS SPLIT TO SHOW DISCOLORATION.

FUSARIUM WILT DISEASE.

. I.
i =,,,

', o,,,,.

Orq
-I
m
x

Bul. 45, Hawaii Agr. Expt. Station.

POTATO LEAVES SHOWING LATE BLIGHT.

PLATE II.

Bul. 45, Hawaii Agr. Expt. Station.

FIG. 1.-ROWS AT LEFT SPRAYED ONCE WITH BORDEAUX MIXTURE,
ROWS IN CENTER NOT SPRAYED.

FIG. 2.-CENTER ROWS SPRAYED, OUTSIDE ROWS NOT SPRAYED.

FIG. 3.-POTATOES PILED FOR COMPARISON.
POTATO SPRAYING EXPERIMENTS.

PLATE III.
MV.474twm '1

Bul. 45, Hawaii Agr. Expt. Station.

PLATE IV.

II

Ii

FIG. I .-SEVEN-ACRE FIELD OF POTATOES IN WHICH LATE BLIGHT WAS CONTROLLED
BY THOROUGH SPRAYING WITH BORDEAUX MIXTURE.

FIG. 2.-YIELD OF 10 AVERAGE HILLS IN ABOVE FIELD; WEIGHT. 171 POUNDS.

Bul. 45. Hawaii Agr. Expt. Station.

FIG. I .-COMPARATIVE TEST OF EARLY ROSE AND HAMAKUA
HYBRID VARIETIES. EARLY ROSE DEAD OF LATE BLIGHT
IN 60 DAYS.

SOME POTATO DISEASES.
Left, cut tuber showing presence of late blight rot; center, black scurf due to Rhizoctonia (causing rosette on aboveground parts); right,
common appearance of Maui potatoes, probably due to IRhizoctonia followed by wireworms, etc.

Bul. 45, Hawaii Agr. Expt. Station.

LEAF ROLL AND ROSETTE ASSOCIATED WITH STEM LESIONS DUE TO RHIZOCTONIA.

zone; on underside of leaf in damp weather a delicate frost-
like mildew may be seen; in wet weather the plants entirely
roti in a few days. Preventive treatment must be given
before disease starts or as soon thereafter as possible; if
plants are badly attacked, spraying will not be worth
while.
Late blight (PI. II and p. 20).

*.

:l." -
*i"7

i' '

I'-
,-,.

i. .: ..

Wilting and rolling of leaves, etc.
Young leaves and new growth first affected. Leaves bronzed
on underside, twisted, and curled up, becoming fuzzy and
drying up, the plant dying from the top downward. Mites
can be found with hand lens. Prevalent in the dry season.
Potato mite disease (Pls. XII and XIII and p. 31).
Plant appears to suffer from lack of water and dies prema-
turely; lower leaves wilt and drop off; interior of lower
stem at ground level shows browning of vascular or woody
portion.
Fusarium wilt (Pl. I and p. 18).
Leaves more or less rolled and tubular; plant spreads out and
grows all to top; tubers few, small, and set close to stem
in a bunch or forced out of the soil; tubers forming in
axils or leaves in advanced cases; stem girdled below
ground with brown cankerous lesion.
(Rosette (Rhizoctonia) (Pls. VII, VIII, and IX and p. 24).
Lower leaves wilt; stem at soil level rotted through or hollow,
with white fungus growth producing mustard-seed-like
sclerotia.
Sclerotium wilt (p. 25).
Leaves roll up in tubular form, or plant wilts and generally
appears as if the stem were broken off; interior of stem
may show burrow of the stem borer, or possibly the plant
is cut at soil level by cutworms.
Borer, cutworms, etc. (Text fig. 5 and p. 30).
r diseases.
Tuber rots.
Field rots.
Burrows with worms inside and soft ill-smelling rot,
following foliage infestation by leaf-mining worm.
Tuber moth (P1. XI and p. 29).
Brown dry rot running just under surface of tuber,
which often has a purple tinge. This is the late
blight rot, usually followed by various soft rot
organisms; it occurs in heavy, cold, wet soils
when late blight has attacked the tops.
o619_.2 Late blight rot (P1. VIII and p. 28).
182264*-19--2

_LO MUJ LaltJLJ.1 I

Thber dtin ed. .... .. *:' l
Tuber rots-Continued. .. ..::::::.,
Storage rots. Wet and dry rots of various appea 6 B
with mycelium-lined cavities and frequently 7) ....
and watery-brownish. These are the Fusarlum r ..-0B
follow wilt infection of plants and most COMN .i.
at the stem end. Slight wounds also furnish e....
the several wound-invading, Fusarium-rottiag. o ag.
Fusarium rots(p
Surface blemishes. ...
Rough, corky scab spots scattered over surface or co .t....
entirely. ..
Corky scab (Text figs. 1 and 2 and P-MI
Small black raised masses resembling dirt on skin; not romw
washed off but easily scraped off with the naiL Badly t'.
tacked tubers roughened and cracked open. A ttabi
occurring simultaneously with rosette and caused brq ..
same organism. :
Black scurf or russet scab (PL VIII and p. 4)10
Numerous small galls and pimples on the surface of the tu..er..
Within the galls are minute, pearly-white, gisten
bodies. If the tuber be cut a row of these g itein
bodies may be traced about one-eighth inch under the pe'LH
Affected tubers rot quickly.
Nematode or gallworm (P1. XIV and p. 3Sh..'
PARASITIC DISKASESL
FusAxruM WILT (Fusarium ozysporum). .,:;
... *i !:::: :
The wilt disease of Irish potatoes caused by the fungus FIGr*Ii&?
oxysporum is prevalent in the principal sections of the islands whkim
this crop is grown. Potatoes from California, both seed and table
stock often used here for seed, are frequently found infected wj&it
this disease. It is the most serious and persistent disease with whiob.
the growers of that State have to contend, and it is highly prohbitel
that the disease was introduced into Hawaii on seed from Califoraii
The disease is characterized by a slight rolling and wilting of tk
leaves and premature drying of the plants. The lower leaves wil
droop, and die first, and the color of the foliage in the early 4t40
may be lighter than usual. As a rule the disease is not evident u"util
the plants are about a foot or more high. The appearance of th!
plants is the same as that of plants suffering from lack of water, &it
this is really the case, even though there is plenty of water in 6ib::i
soil. Upon splitting, the woody portion of the underground ste.a'
is seen to be discolored, that is, more or less browned (PL I, fig.-2)*
The fungus Fusarium oxysporum enters the plant either from, 0
seed or from the soil through the smaller roots and works its Awgi
up through the water-carrying vessels of the roots and stem, .a
often later through the stolons into the young developing tu.bl4
(PI. I, fig. 1). The fungus mechanically obstructs the water" duati

.

ajts. J,

low JU'.!

POTATO DISEASES IN HAWAII. 19
| or.s a V=01 system and limits the amount of water available to the
Plant. Whether there are other injuries to the plant through se-
I retions of harmful products by the fungus has not been demon-
strated.
The wilt disease results when seed carrying the disease is used or
I when healthy seed is planted upon soils already infected with the
Parasite. With continuous cropping the disease becomes more ser-
ious from year to year until finally, unless seed selection and crop
Rotation are practiced, potatoes can no longer be profitably grown.
Some of the fields in Maui appear to have reached this stage, partly
from soil exhaustion. The plants die and dry up shortly after
blossoming, and the tubers remain small and only partly developed.
The fact that Fusarium wilt may be readily overlooked, the prema-
ture drying of the plants being mistaken for the natural result of
prevailing weather conditions, constitutes an insidious danger, since
diseased plants yield a preponderance of small unmarketable tubers,
which, according to the Hawaiian method of marketing, are kept
for seed, the large and medium sized tubers being sold. The result
of this practice and of continuous cropping is that only in an
occasional season can anything like a satisfactory crop be raised in
fields where this disease is established.
Control.-The control measures which have been suggested for
this disease consist chiefly of seed selection and crop rotation.
Neither of these measures will entirely eliminate the wilt fungus,
nor is it probable that a rotation of less than three years will ap-
preciably improve badly infected fields, but it is expected that in
the absence of susceptible crops for a three-year period the virulence
of the disease will be reduced and one crop of potatoes can then be
grown profitably provided healthy seed be used.
Seed from disease-free fields should be obtained whenever possible.
If imported seed is used, it should be secured from regions where
this disease is not prevalent and certified seed should be insisted
upon (see p. 4).
Detection of wilt infection in seed.-The following is a useful
though not absolutely sure means of detecting the presence of the
wilt parasite in seed potatoes. The stem ends of a large number of
the tubers to be tested are cut across with a knife, exposing the flesh
Within the tuber where the woody fibers from the stolon rootlikee
| stem to which the tuber is attached while growing) spread out to
Form the tuber ring. If a dark-colored or brown ring appears or
|brown fibers penetrate the flesh at this point (Pl. I, fig. 1), the tuber
Should be considered highly suspicious. If many tubers show such
R.a discoloration, the whole lot should be rejected for seed purposes.
Consider g the prevalence of wilt infection in most available seed,
it is advisable to cut off and discard the stem ends of all seed planted.

%0 flAJjJL..., XLWa1. iiLr.La JNIm J nJ

This test for wilt.is not absolutely sure, 0as not al, tubei-
the wilt disease show the discoloration sufficiently "*to-;
nitely the presence of the fungus. Certain other dLIMeS
somewhat similar discoloration, and in some cases tubers
slight yellowing of the vascular ring which appears to fe ,,,liir ,
period of dormancy and to be unassociated with disease: ',i
event these doubtful tubers are not desirable types to proi1agat:..i
.. .:- .... ......A:.
LATE BLIGHT (Phytophthora infeatans). .....
.p
No disease of the Irish potato is more destructive than :Bthe
blight when the conditions favor its development. Late bgi, '
caused by the fungus Phytophthora infestans. The name late. Uba
was probably given to this disease to indicate that it ocurseAi
commonly late in the year and to contrast it with the early .b31|iW
(Alternaria solaMi) which is prevalent in the dry weather f :tu
summer. It is apparent that the 'common names of these tmw
eases are without significance in Hawaii. The names dry blight 4
wet blight for early blight and late blight, respectively, aretbg,.
to be locally more appropriate common names. ?ii Aj
Wet blight, or late blight, is widely prevalent and destructide ';:!
the Hawaiian Islands. It seems probable that this disease and WiM
wilt disease (Fusariuln oxysporum) are the most potent faetonS0i
lessening yields and discouraging potato growing in these islaith
When the late blight appeared in Ireland in the middle of theWaiAl
century it so devastated the potato crops, upon which the pe4...
largely depended for food, that famine resulted. Since that .1 ei4'"ii
disease has become prevalent in many of the potato sections 'o:ftif6
world, and it has been the object of special investigation where 9
occurs. Various means have been devised for its control, but t'th*!
is no ground for hope that it can be exterminated, and potato grows.
will probably always have to contend with it. "" .:MN
The disease is manifested in the leaves by dark, more. or iiW
rounded, water-soaked spots or areas (P1. II), which may;-or 07.i|
not increase rapidly in size and number, according to weather oNa`
editions. Upon the lower surface of the leaves of affected Po
growing in damp situations a characteristic delicate frostlike :id i'
dew appears. This is the parasitic fungus bearing its microsmpt
spores. The latter are minute seedlike bodies which, spattered :-Aie
by rain or transferred by contact of the leaves with adjacent mei*i
foliage, carry the disease from plant to plant. In this way a:
eased spot upon one leaf may serve to infect a whole field in M
credibly short time. Similarly the spores falling and being w
upon the ground find their way to the developing tubers whiifh..
may infect, causing them to rot in the ground or subseqia
storage (P1. VIII). With continued dry weather the spots uponhl 7

Y J3 ULJALJ

POTATO DISEASES IN HAWAII.

r Iaves remain about the same size or spread slowly, but with heavy
I dews or rainy weather the disease progresses rapidly. In a few days
I the foliage may be all rotted away, the layman perhaps having over-
Slooked the first few spots and being inclined to attribute the trouble
i: to the rain or the hot sun following the rain, etc. In Hawaii, pro-
tracted hot weather is sometimes observed to control the disease
completely.
Weather conditions which favor this blight are as follows:
High relative humidity, low soil temperature, and a high moisture
content of the soil. Since such general conditions frequently prevail
in the main potato sections of Hawaii, this disease may be expected
to appear on almost every crop planted in these localities. Such
is the rule. In some places one crop a year may suffer less than the
others. The damage from this disease is popularly supposed to
be due to the hot sun shining upon wet foliage following light
sprinkling rains. There is no question that the major portion of
the trouble thus described is the wet or late blight, and not sunscald
or tipburn.
In the islands the wet blight is probably carried from crop to
crop, as these follow each other almost continuously in the same or
adjacent fields, largely by volunteer plants. Where any sort of
rotation is practiced, volunteer potato plants are allowed to mature
and are dug. This custom will have to be discouraged in any at-
tempt to control diseases and insect pests.
Control.-The control measures worked out for this disease con-
sist entirely of methods of preventing infection. Healthy and
vigorous seed stock and rotation of crops are important. Fortu-
nately, Bordeaux mixture, applied thoroughly and in time to the
foliage, has proved beneficial in controlling this disease (PIs. III
and IV). The insoluble copper in the mixture gradually becomes
soluble and prevents the germination of the spores of the fungus
which fall on the moist leaves. To be effective the spray must cover
the entire surface of the foliage, and it must be there before the
spores find lodgment. After infection has taken place, the parasite
is out of reach of the spray.
The practical application of Bordeaux mixture to many of the
larger fields is being rapidly worked out. In some sections where
the blight is most destructive and where the potato would otherwise
be at its best, as in the Glenwood section of Hawaii, the frequent
and excessive rains make thorough and timely spraying an uncer-
tain and, for the most part, an impossible matter. Even under these
conditions, spraying may afford some relief when the weather con-
ditions are such as to permit the spray to dry. The Hamakua
Hybrid potato promises to resist the blight under the conditions at

21

..** : ? !',
Gilenwood, and there is every indication that Athit>-irtiy ir
the blight problem for such districts. ,*oM^
The spraying with Bordeaux mixture thus far carried -o:,b:!!j7
writer and his associates for the prevention of wet bli .ti i
blight has resulted in an increase in the crop of from50, S Ut...
cent by weight. (See Pis. III and IV.) ; I
Resistant varieties.-For many years attention has been i .......
to the development of varieties resistant to the late blight inru" ,
and on the mainland of the United States, but thus farth
striking success. Varieties showing resistance have been typesoi6A
in demand on the American markets. : ,El
A type of potato originated by Miss Yamata, of Honokaa, HaiL ig
is reported to be much more successfully grown in that locality t.iblj
any other sort. This type of resistant potato, of which themei a'ia
two strains, has received the name Hamakua Hybrid from bla:Yh..8i
*r....., ..... ;.. -*':'.::!,!!
trict in which it first came to the attention of the station. .
parent of both strains appears to have been the local variety ij
as the Portuguese Purple, originally brought to the islaadsz.tii
Portuguese immigrants. One form of the Hybrid is a white awlfii i
purple mottled tuber, of the general shape of a Burbank, with *:atI:wf.
deep sprouts and eyes. The other, possibly a cross between:. ..
Portuguese Purple and the Early Rose, has a pink spin and puxpe,:ii
eyes and sprouts, and is a more desirable tuber for market. :.. ,,:
Practical results support the view that this Hybrid has a proFi.i.si.
~ ~ ~ ....... .::" ..' i!
ing degree of resistance to late blight in these islands, but experiment |
evidence is somewhat conflicting. At Glenwood two experiments
different workers have shown its practical value in that diati ..,
Four acres of the variety grown in this section yielded over "400 bari(.
of 100 pounds each. At Castner a small patch of the Hybrid aund.ke':
Portuguese Purple varieties planted October 20, 1917, was unaffeetiw .
by late blight on February 1, 1918, when other potatoes planted at
the same time within a few hundred feet were devastated by'Vt [:
disease. The grower stated that Burbank potatoes planted at: tb|li
same time as the Hybrid and adjoining them were all dead in SQ|
days. The Hybrid, therefore, grew through a period of im ian s iji
than three months of weather suitable for late blight. They ,sho.1Wid-:.,,:::.
some early blight spots but no trace of the late blight disease. ; i
In order to test the blight resistance of the Hamakua Hybri-4, it'::i:
was also grown in comparison with the Early Rose variety in a s:aWB..
plat at Castner substation (P1. V). Owing to the poor soil theipi..
the yield of neither variety is normal, but the resistance of the ,Hihmw.ti
kua Hybrid to late blight is striking. Both varieties grew well :i
first month, but at the end of 60 days the tops of the Early Rose hadi-
been destroyed by the late blight (P1. V), the 96 hills yieldingqttjJ0
74 pounds of tubers the size of marbles. The Hamakua Hybrid X
.. .Wi

POTATO DISEASES IN HAWAII. 23
Smained almost without a trace of blight spots, and at the end of the
fourth month 20 hills were dug, yielding 94 pounds of fair-sized
Stubers. The Hamakua Hybrid grew through weather favorable-to
Slight for most of the period of the experiment.
I -It appears from the foregoing that the Hamakua Hybrid and one
Sof its parents, the Portuguese Purple, possess a real resistance to
Sthe late blight under Hawaiian conditions. Should the indicated re-
Ssistance to late blight of the Hamakua Hybrid be of more than local
Importance, the quality of the tubers can doubtless be improved by
selection in the direction of market requirements, though there is not
the discrimination here against colored and long potatoes that is
characteristic of the eastern markets.
I
EAnLY BLIGHT OR DRY BLIGHT (Alternaria solani).
Early or dry blight, a fungus disease (P1. VI) attacking only the
foliage of the potato and producing a characteristic spotting and
death of the leaves, is prevalent in the Territory in dry, hot seasons
and occasionally may cause a loss of from 5 to 25 per cent of the crop
in affected fields. As previously noted, the name" early blight" as ap-
plied to this disease on the mainland has little significance in Hawaii,
unless it be that the disease attacks the plants earlier in their period of
growth than is characteristic of the late or wet-weather blight. As
previously noted, the name dry blight or dry-weather blight is locally
more appropriate for this disease.
The parasitic fungus produces circular to more or less angular,
dry, brown leaf spots, often with concentric markings with something
of the appearance of a target (P1. VI). The spots are from one-
sixteenth to one-fourth inch in diameter and sometimes confluent, and
frequently the dry tissue falls out, giving a shot- hole effect to the
leaves. The spread of the spot may be limited in certain directions
by the leaf veins, in which case it is more or less angular in shape.
The spots caused by the dry blight are from the first dry and brown
Sand the progress of the disease is comparatively slow. The badly
affected leaves dry and die after a few weeks. The stems and tubers
are not directly affected, but as a result of defoliation and early
?-maturity of the plant the yield is materially reduced.
S Early or dry blight appears to be only occasionally serious in the
3 islands. The prolonged drought during the summer and fall of 1917
in the Hamakua district of the island of Hawaii was particularly
favorable to its development. A loss of 25 per cent was observed
in some cases, most of it due apparently to this disease, though the
mite disease, subsequently to be discussed, and bud and leaf infesta-
tion with the tuber moth were undoubtedly responsible for a portion
of the damage.

,if.. ULI ,.A. J .J.AA EA 7 *JIL fTl J.La 'J'CI'HC"A J 'I.. I ,MJL .. :CI .Lfl'tiifLl H' L. 2J x q.J
14n .... 04'.: ;;.
Control.-The experience of investigators on the. ls
shown that dry blight can be controlled by timely d4W
spraying with Bordeaux mixture. Where the condition .: a.."
vorable to the development and spread of this malady., ,^tbti-: ^
should be sprayed as recommended for the late or wet b-ligkh.
a general practice, potato plants in the islands should be$p
from three to six times per crop with Bordeaux mixture,........
sprayings being required in dry seasons than in wet seasons. I,..
former case the spray will prevent the attacks of the earlyo:rw
blight and in the latter the attacks of the late or wet blight. A la
BLACK SCURF (RussET SCAB) AND ROSETwrE (Rhizoctoa solani). 6 4' ,
.. .... :,:: .: ,
The diseases of the potato commonly attributed to the parasitiii..
fungus Rhizoctonia are quite diverse in their general aspects or' .
signs, but they are conveniently grouped together for discuion. ;
The Rhizoctonia fungus is a soil inhabitant which attacks the udesr "4?
ground stem and roots of the plant (P1. VII) with effects vary" ig ;
according to the portion injured. 1
Black scurf is the name commonly applied to the black ac
.'- r j 1: :' !
lated mycelial masses or sclerotia of the fungus which adhere de14 .' ..
to the skin of the tuber in such a way as to be readily mistaken,- 4r'
bits of soil. (See P1. VIII.) They do not wash off easily, althqji ..
they are superficial and readily scraped off with the finger nafl:':n
This stage of the fungus does little damage other than to the appqa::
ance of the tuber, but it is by this resisting stage of the parasite tut .
the disease is largely spread to new land and to new localities. j
If tubers affected with the black scurf are planted, the spril
'*. )., .. .... *""***j !l
may be attacked and girdled by the vegetative threads of the ......i..,
As a result of this action the. following types of disease may o.cur: ,
Weak plants: The fungus kills or injuries the sprouts and a. poor $ iI
and weak plants result (PI. VII, fig. 1). '
Rosette disease and leaf roll: The leaves of the plant become light grTO: J:
and roll upward on the midrib as an axis, becoming tubular (P1. IX). %iEA^ 4.
plants may be more or less dwarfed. The few undersized tubers whidh f i. :1
are set close to the stem, often pushing out of the ground (PL. VII, fig. 2).. :;^
Aerial tubers: The stem below ground is girdled more or less compet.ei ,*'
The food elaborated in the leaves and designed for subterranean tuber foraMl-.
*-* ." y f i *- "
tion is diverted, and tubers form above ground in the leaf axils (PI. X). r:I
Growth to top: The stolons or stems of the young tubers are attacketiby' .
the fungus and the young tubers being partially cut off from nourishment.ll :fi ,
to develop normally. The plant nay develop luxuriantly and yield only .ew:;;|
small tubers.. -. :...:
Disfigured tubers: The tubers are frequently covered with the black .iscud.
or sclerotial resting stage of the fungus. The same stage of the fungus is bS.;;.
lived commonly to be responsible for rough brownish and russet areas on the El t
face of the tubers. Throughout such areas the skin is finely and irreguln&iitF
cracked. Large cracks in tubers are also attributed to the action of this orgauiz i
as well as to uneven growth, and deep pit-like holes often occur which may:':.
caused by this fungus (PI. VIII). .':.|
.... "".il.

oi 1 I 1WII i

.. :... ... "

POTATO DISEASES IN HAWAII. 25

S-The name Rhizoctonia, as used -here, is a group name for a number
of cosely related forms. This sort of fungus is a soil inhabitant
: which is thought to be favored by heavy, wet, sour soils, but in these
|islands it appears to be responsible for considerable damage even
.; on porous, light, well-drained soils.
Iontrol.-The measures found effective in controlling this soil
Is organism are seed selection and seed disinfection in corrosive-subli-
mate solution (p. 9), combined with planting in uninfected soils or
Ssoils in which the liability of infection has been reduced by crop
rotation. Root crops such as turnips and beets are susceptible to the
parasite and should not be used in the rotation. The Rhizoctonia
types of injury are very prevalent in Hawaiian fields, and attention
to the control of these diseases will have to be given before any great
increase in yield can be had in some localities.
SCLEROTIUM WILT (Sclerotium rolfsii).
The Sclerotium wilt disease is caused by the fungus Sclerotium
rolfsii, described by Rolfs1 as the cause of a wilt of tomato in Florida.
Besides the tomato, this fungus causes a similar disease of the fol-
lowing plants: Potato, peanut, eggplant, bean, cowpea, summer
squash, cabbage, beet, and melon. It is reported to be very destructive
to the Irish potato in heavy, wet soils. This fungus has been isolated
from diseased peanuts growing on the farm of the College of Hawaii,
SOahu, and also from Hilo, Hawaii, but as yet Irish potatoes attacked
by this disease in the islands have not come under the writer's ob-
servation. Larsen describes it as occurring on potatoes in the vicinity
of Honolulu in 1913. He isolated the fungus and performed suc-
cessful inoculations on potato plants. Since his publication is not
generally available, and this disease is likely to be of occasional im-
portance in some localities on the islands, the following quotation
from his description is given:
Sometime last January (1913) our attention was called to a field of po-
tatoes in the vicinity of Honolulu which was being entirely destroyed as a
result of some disease while the plants were still immature. On investigation
it was found that the field in question, covering some 2 acres, was affected
with a fungus malady known to mycologists as sclerotial disease. The same
trouble was then found in other potato patches about Honolulu and occasion-
ally on other host plants as.well. In most cases the trouble was fatal to the
affected plants, causing severe loss wherever it occurred.
The first indication of sclerotial disease is a slight drooping of some of the
m younger leaves and leaf tips. On succeeding days the wilting becomes more
Pronounced, until in the course of two to four days the entire shoot wilts and
fails to recover. Sometimes several or all the shoots wilt simultane-
Sously. At the first indication of wilt, if one examines the base of an affected
shoot, just below, and sometimes also a little above, the surface of the soil, one
will find that the outer tissue through the cambium is decayed. The
decayed area may or may not extend clear around the stem. Eventually the
SRolfs, P. H. Tomato diseases. Florida Sta. Bul. 117 (1913), p. 40.

fungus travels inward, past the woody bundles and ac .. .
which then falls over as if broken at the base. Even before th.is 'w1
place the disease will have penetrated beyond the woodt asr
the soft and watery core, in which it travels upward and dovii M
rapidity. The core tissue is quickly discolored and soon d:
woody circle of vascular tissue like a hollow skeleton of the.Qi'g. !
During moist weather conditions, a white mycellal growth uayi1n 1i11"A
the affected tissue and in the hollow stem, and white mycelial strana.':i
oqcur in the soil surrounding the plant. This mycelium soon produces ,
white tufts, which become round, smooth, and hard, and change froiz 'IM4
yellow, then finally to dark brown. Such hardened mycelial mass iare
as sclerotia. They are the only reliable means of identifying the pM
When mature and dry they resemble mustard seed both in sizean4c
During dry weather these sclerotia do not develop under natural odiq
and artificial means may be adopted to induce their formation in ordtiW'1i
diagnose the disease. This can be done by placing one of the affected ,hdlhlt
in a moist chamber *. "... '.*..O .\.
Larsen records alfalfa, coreopsis, taro, and Irish potato as affeetd.
with sclerotium in these islands.
Control.-Rolfs1 found the Sclerotium disease of tomatoMs s:. i
ceptible of treatment with some soluble form of fungicidehu .. g'b2:a
an ammoniacal solution of copper carbonate or eau celeste. '
writes as follows regarding this means of treatment, which is '..
z .. :. ," : f:
successful in Florida: ... .. "..:
One of these fungicides, preferably the ammoniacal solution of cpp j|
bonate, should be sprayed on the soil about the stem of the plant. By 0prqy ."||
on a half teacupful at this point the plant is usually perfectly protected aiSI
infection. In using this remedy it should be remembered that whe.........
fungus has gained entrance into the tissues of a plant before the agictM\'
.-A
has been applied, the remedy will be of no avail. '".i "i&
The formula and description of preparation of the two -ngiMtj1
solutions is given on pages '13 and 14. As an additional meaib&4"'
controlling the ravages of the fungus, the soil about the plants shitIi
be loosened and exposed to the action of the sun and air. In drtn
weather this serves to kill the fungus to some extent, thus pre tiino
infection.
iL i
COMMON OR CORKY SCAB (Actinomyces clhromogenus). ..:...
: ; .....: :: .: ... .
The disease known as common or corky scab attacks the g'o w i:i"
tubers at any stage of development (figs. 1 A and 2 B). Th eii
of infection are first evident as small brownish spots on the S.Ail.
face of the tuber. The spots increase rapidly in size and dept.
until the whole surface may become covered with the nisig
rough, scabby areas. In some cases the potatoes crack open or-t.it
spots are enlarged and deepened by insects. The scabs ConMii
accumulated corky tissue formed by the tuber in an attemptto" p'"
tect the underlying tender tissues from the irritating action o:e:b
I Rolfs, P. H. Tomato diseases. Florida Sta. Bul. 117 (1913), p. 41. '4.
'".:**:i "g
"::.. :"' .***..

S.... POTATO DISEASES IN HAWAII. 27

oaroipeching fungus. This disease is caused by a bacterial-like or-
Sganis until recently known under the name Oospora scabies, but
its, relationship to another group of fungi having been shown, it is
Snow called A ctinomyces chromogenwus.
SThe corky scab disease not only reduces the value of the crop but
i also appreciably lessens the yield. The losses through decreased
Yield have been estimated variously. For example, Goff1 planted
Equal amounts of very scabby seed and seed free from scab on a soil
which had been in clover sod. The scabby seed yielded 1991 pounds
and the scab-free seed 477:1 pounds. The decreased yield is brought
about through the failure of the seed to germinate and the lowered
vitality of the plants. The value of the crop is reduced in several
o ways. The unsightliness of scabby potatoes and their changed taste
and odor lower their market value. The increased liability to tuber
decay and the the extra thick paring necessary in preparing the
potato for the table result in considerable loss to the consumer.
This disease is not very prevalent in the islands, but at times on
poorly drained, hard-packed soils or soils which have been limed
it is more or less troublesome and probably the source of considerable
loss.
ControL.-Seed selection and disinfection, certain types of ferti-
lization and soil treatment, and crop rotation have been found more
or less successful in preventing the common or corky scab. The
organism causing the disease is distributed for the most part by the
use of scabby seed potatoes, and only scab-free tubers should be used
for seed. To reduce the probability that scab organisms are carried
to the soil by the seed, the latter should always be dipped in one of
the potato-seed disinfecting solutions (p. 9).
Scabby and refuse potatoes should not be fed to farm animals if
the manure from these animals is to be scattered on the potato land,
as it has been demonstrated that the organism can survive passage
through the alimentary tract of animals.
The development of the scab is favored by a high humus content of
the soil and also by an alkaline reaction. To the latter fact may be
attributed the unfavorable results of adding lime or wood ashes to
? potato soils. Halsted obtained favorable results by fertilizing with
kainit (Stassfurt salt containing 20 per cent potash). According to
Beekwith and Taft4 muriate and sulphate of potash also reduce scab
Injury. The plowing in of green manure and, in fact, any cultural
Practice which tends to make the soil acid will reduce the common
or corky scab on badly infected fields. Crop rotation has been sug-
SGoff. E. S. Experiments in potato culture. Wisconsin Sta. Rpt. 1892, pp. 278-280.
SHalstead, B. D. Field experiments with potatoes, I. New Jersey Sta. Bul. 112 (1895),
pp. 1-12; Rpt. 1896, pp. 309-315.
SBeckwith, M. H. Potato scab. New York State Sta. Rpt. 1887, pp. 307-315.
'Ta&ft, L. R. [Potato scab.] Michigan Sta. BuL 57 .(1890), pp. 23-25.

28 BULLETIN 46, HAWAII EXPEMMEJWT -STATOS.':4,
*t
gested with the assumption that in the absence of- tiw* p .."....
number of years the organism would die out. ITMasmuch-acti
beets, and other root crops are susceptible to attack tlhiy
be included in the rotation, as they would serve to cary otw j|
MY,,
disease. "
POTATO TUBER ROTS (Phytophtkhora infestans, Fusarium orawr *,.' l
F. radioicola and F. coeruleum), .* .u* ft...
In spite of the fact that the major part of the potato crop a: -
islands is consumed soon after the tubers are dug, the total sa
loss by rotting is an item of considerable importance. It is a sena
source of trouble in keeping seed stock and often results in the tS
of inferior tubers for this purpose.
The type of rot most commonly observed is often called dr'y OP
though this name is frequently misleading, as the nature of the i4
depends upon the amount of moisture and upon the ter
With plenty of moisture and a moderately warm temperature tJ
rot develops rapidly and is of the soft type. If the rot Aevt
more slowly, or if wet rotting tubers dry out, the typiqda7"'- ti
phase is produced. These forms of rot are caused for the mnstA
part by three species of Fusarium known as F. oxysporum, F. ni-t::
cicola, and F. coeruleum. Rotting of the tubers is very prevanati::ai:
the crop from wilt-infected vines. : ..j*.,1
Another tuber rot is caused by the late blight fungus. Whenutb|:
tops are destroyed by this blight, the tubers may rot badly il ti"c
ground. The spores of the fungus are washed from the legvav.*m
the ground and thence to the tubers, which are infected. This rot4
is a firm brown discoloration extending through the surface layers 4 I
the tuber a short distance beneath the skin. In the earliest s-ags
it shows through the skin as a slight brownish or purplish area, whri&
later becomes more or less shrunken. In heavy, cold, wet soils ti4i,
rot spreads rapidly through the tuber, and a soft, ill-smelling, secoode.i:
ary rot caused by bacteria hastens the destruction. In drier soilt!
little evidence of rot may be present, and yet the tubers, if infted$pil
will rot badly in storage. ,
Control.-The rotting of potatoes can be largely controlled: by;r;
storage at a temperature of about 35 F., and where low temperature ,
facilities are at hand such storage offers a practical means of oiw;:
serving the potato crop. However, even at this temperature the rtnia
progress slowly, and for best results the tubers should be carefuuy
sorted before being put into storage. Storage facilities at suobh1 pg
temperature are rarely available to Hawaiian growers, and at pr.': |
ent little advantage can be taken of this method of holding the c:r Ip
or seed tubers. To prevent loss through rotting under conditiongiwd,
the islands, attention should be directed toward the prevention ef6 ini,
"""i

A..

I !feetion through the use of good seed, crop rotation, control of
. eases and insect pests as far as possible, careful handling of
f crop, and storage at the lowest available temperature.
TurBE MOTH (Phthorimoea operoulella).

29

dis-
the

The tuber moth is the most serious insect pest of the Irish potato
in Hawaii because of the damage it does and the difficulty with which
it can be controlled. It ranks second only to late blight as a poten-
tial pest of this crop, though the conditions favorable to the one are
unfavorable to the other. This insect also attacks tomato, eggplant,
and tobacco (as splitworni), though less actively than it does the
potato.
The moth, which is small and grayish in color (fig. 4), lays its
eggs upon the leaves or other parts of the plant. The larve or

worms quickly enter the
leaves, mining between
the surfaces, or bore
into the stem or tubers
(P1. XI). Affected
tubers soon rot, due to
invasion by one or more
of the numerous wound
bacteria or fungi. In
Hawaii there are prob-
the year. The moth is

most prevalent during the dry season, that is, from May to October.
The damage it does in drought years is almost unbelievable.
Control.-The tuber moth is very difficult to control, even under
the best systems of potato culture, and the regrettable lack of system
Sin Hawaii greatly increases the difficulties. With potatoes growing
S in every month of the year, with practically no rotation in general,
S and with volunteer potatoes allowed to mature with corn or beans,
etc., where an indifferent rotation obtains, the outlook is not encour-
aging. The procedure outlined on the mainland for the control of
this pest is cited below, and as far as practicable these methods should
Sbe followed.
Clean cultivation: A411 volunteer potato plants as well as all solanaceous weeds
should be pulled out and destroyed. When a potato crop is harvested the vines
and all small tubers should be gathered up and burned.
Crop rotation: Crop rotation is essential, and the cooperation of all growers
: of a section is necessary. Crops which can be used in rotation with potatoes
are beans, peas, corn, cowpeas, alfalfa, and clover.
Hilling: Hilling up the potato plants much more than is generally practiced
hee, thus increasing the depth of the tubers, will probably help to prevent tuber
Sinfestation during the maturing of the crop.
N Digging and sorting: The crop should be dug as soon as mature and brought
In from the field before late afternoon. If the tubers are infested, as is indi-

POTATO DISEASES IN HAWAII.

I

cated .by mining .often..v4as"k just,:.ul.r, u tu, .ao-" skulael ,#* kt.
the eyes, they should be carefully sorted at once. Those I ..steds..|..
either destroyed immediately by burning or fumigated if' they are
as stock feed. Those still unimpaired should be fumigated as": i )
and placed out of reach of the moths and of further infestation. '*" :
Fumigation: Place the tubers to be fumigated in a room that can :.beii
For every 1,000 cubic feet of space to be fumigated place from 1 .t0.I
of carbon bisulphid in a shallow dish or pan and set it in the top of: :O
The amount of the chemical varies with the tightness of the room. Wor w
containers the following amounts are recommended: Ten-gallon "'sake's ,l H
one-tenth to one-fifth ounce; 50-gallon wine barrel, one-half to 1 ounces A
chemical is placed in the top of the room or container, seal up immed.iat.ly|.:
leave undisturbed for 24 hours. Remove and ventilate the material for R ; -
time and place in moth-proof storage, if possible. If the potatoes are h1.III
storage for any length of time- they should be examined at frequent intervaisr'.
further infestation and treated again if necessary. Seed potatoes may 'be :fwigt....
gated if the lot is suspected of containing worm-infested tubers. They.mlU i"l: .
fumigated before the sprouts are prominent, as otherwise the tubers will .|
,. r..* :' !i:
killed. Carbon bisulphid is volatile and highly inflammable. Keep awm frt,1
fire. The fumes are poisonous. Do not inhale. .:": "
< ,.. .. t ,"c. ".. S
Spraying: The use of Paris green or other arsenicals in Bordeaux .I ......
(p. 10) when the latter is being regularly applied *will probably b 'Nftw.... :
benefit in combating the tuber moth. .. -
:::.. .. ..: .
CUTWORMS, ARMY WORMS OR "POKOS," SNAILS, ETC. |
*... *" j ii .'
Of insects injurious to potatoes, the cutworms (fig. 5), especially|
the leaf-eating form locally known as "poko," rank next to the tubo'riZ
-/ 6;;:;

L odl : The "poko" in the early summer months is a voracious
Ifeeder, and unless it is checked by artificial means it may entirely
I destroy the foliage of the potato vines. The "pokos" as well as
Sthe true cutworms are night feeders, which during the day may
Usually be found curled up in the soil at the base of the plant upon
which they are feeding.
Control.-The growers of potatoes in the islands have been quite
successful in controlling these worms with a poison bait. Before
the war it was customary to use a bait made of the highest grade
of wheat flour and Paris green, a high grade of flour having been
found economical by the farmers because it is finer and can be spread
more thoroughly over the vines and over more plants than the
coarser grades. The poisoned flour is dusted in the late afternoon
over the plants and the soil at the base of the same. Some burn-
ing of the foliage, or arsenical poisoning, results, but this is usually
not serious (p. 35). This treatment is generally used and is con-
sidered effective by the growers. The cost of the flour used is a
not inconsiderable factor in the expense of growing the crop. As
a substitute method for the control of these pests, the poison baits
of which the formulas are given on page 14 are now being success-
fully used. It seems probable that the leaf-eating worms could be
controlled by the use of arsenicals with Bordeaux mixture (p. 13).
Paris green is used at the rate of 1 pound to 50 gallons of Bordeaux.
Where Paris green is used the burning of the foliage is prevented
by the life in the Bordeaux, or, if necessary, an additional quantity
of lime, equivalent to the amount of Paris green used, may be added
for the purpose of neutralizing the free arsenious acid.
MITE DISEASE.

Irish potatoes growing in Hawaii in dry, hot situations, whether
irrigated or not, are frequently seen to dry up and die from the
growing tip downward. The small young leaves turn brown or
become bronzed on the under surface, get abnormally fuzzy," and
twist or curl up, and soon the shoots and leaves dry up and die
(PI. XII). Often the plants grow well until about the time of
flowering, when they gradually dry up and die prematurely. The
yield of such plants is negligible. The young growth is found upon
examination to be attacked by a multitude of minute mites, which are
Scarcely to be seen with a hand lens having a magnification of less
|S *than 20. These pests suck the juice from the tender foliage and
Ultimately kill it.
I This disease of the Irish potato seems to be a new one; at least the
w: riter has been unable to find such a malady mentioned in the litera-
ture. A somewhat related disease is described under the name

"phytoptosis on the tomato in Florida by:- tlfs.1 Tie s aE
ing the potato is quite different from the one found by...-...
ever, this being Eriophyes or Phytoptus, while that A.t..jW ....
probably belongs to the same group as the -so-called .
(Tetranychidae). I .
The mite disease was first noted by the writer early in Mayi,
in the vicinity of Honolulu and Castner, Oahu. It was sodnf
:,..:: o n "A.': ,,i
to be very prevalent and destructive after the weather bee:m&t)
dry and warm for the late blight disease. It is now recogniadkgi:
disease of considerable importance during dry seasons in this's=
potato sections, and has probably been destructive to the potato &0
for many years. During the drought of the summer and fall of iSlW
this disease caused losses estimated at as high as 25 per cent in.MAiMWt
fields in the Hamakua district of Hawaii and the Makawao andl ," iw
districts of Maui. Practically total losses were observed inga-a.d
in the vicinity of Honolulu, where the conditions were not favorab 'i
to the crop, the weather being too dry and warm. i..
That this disease is caused by mites is established by the followiigS
facts: These organisms are always present in sufficient numbeftVirie
plants with the recognized symptoms to be considered responsible A
for the trouble; the reaction of the plant is such as has come toIM:.
associated with mite injury; if the mites are kept off potato :p'tait
by spraying or dusting with sulphur the plants grow normally,: W: ..if..l2.
adjacent unprotected rows are devastated; increases in yield df tbSklt
of 100 per cent by weight have been obtained by spraying wifthuia
sulphur. (See PI. XIII.) ,i
The mites are oval shaped and almost colorless when young; 1w'
coming slightly brownish with maturity. When young they haiid
three pairs of legs, later four pairs (P1. XII). The eggs, which a
numerous on the affected leaves, are sculptured or papillate. ;,i
Control.-Experiments (P1. XIII) have shown that the miidip
ease can be almost if not entirely prevented by dusting the p.
with sulphur or spraying them with a lime-sulphur spray. In 9.
warm weather watch the potato plants carefully, and as soon as.
of the small young leaves at the tip show signs of turning brown q:,
becoming bronzed on the under surface, spray the entire surface*q|
the plants with the lime-sulphur spray (p. 13) or dust the. pl.atq
thoroughly with dry sulphur. Repeat as often as necessary.- .$
The mite disease is entirely different in its symptoms from0..
late blight or wet blight disease and likewise from the early ior Id
blight, and there should be no confusion of these types. The, .Ae.
disease can be confused with Fusarium wilt or other wilt d" ......
unless careful examination is made. It seems that there has....,i
Rolfs, P. H. [Tomato diseases.] Florida Sta. Buls. 21 (1898), pp. 23, 24; 47 ( .
pp. 143, 144. 7..* ,,' .|
5:
.*' # "E

; POTATO DISEASES IN HAWAII. 83

confusion of these forms, and it is hoped that the descriptions of dis-
eases herein will help the grower to distinguish them in order that
&the proper treatment may be applied. Bordeaux mixture, which is so
Serviceable as a preventive spray for the two blights above men-
tioned, will keep the mites off the plants for from one to two weeks,
Sbut eventually sprayed plants are as badly affected as if they had
::received no treatment. Sulphur, on the other hand, is effective
against mites, but it is not to be recommended for the late blight if
it is possible to use Bordeaux mixture.
NEMATODES (GALLWORMS OR EELWOBMS).
The potato gallworm or eelworm, one of a large number of species
of nematodes, is a factor of considerable importance in potato pro-
duction in Hawaii. These minute pests are not insects but micro-
scopic round worms. The same sort of parasite is responsible for the
rootknot disease of various crops. The gallworm attacks the tubers
Sand causes the skin to become roughened or cracked and covered with
irregular galls or pimples (P1. XIV, fig. 1). Badly infested tubers
shrivel up, remain partly developed, and become soft and otherwise
unfit for table use. When broken across, such tubers show a line of
glistening specks just beneath the skin (P1. XIV, fig. 2). These are
the encysted nematodes.
There are few cultivated crops not subject to attack by species of
gallworms, and when once established in a field their elimination is
practically impossible. In greenhouses they can be killed by steam
sterilization, but in the open field this is seldom practicable. They
are carried into new soils by infested seed tubers, nursery stock, etc.
Infested seed potatoes, which are of course unfit for planting, con-
stitute a serious menace to the potato industry.
Gallworm injury to garden crops has been observed on Hawaii,
Maui, and Oahu. A general infestation of fields with these pests
would be disastrous, and it is essential that their spread be limited
so far as possible. The cultivated fields of the Territory which are
infested will be determined as opportunity permits and crops sug-
i tested for rotation where possible.
Control.-Seed potatoes should be carefully examined for the pres-
encoof nematode galls before planting. As far as possible, seed stock
should be secured from fields known to be free from this pest. Break
;open any suspicious looking tubers and examine the outer third of the
| flesh for minute brownish spots with pearly white centers. In case of
doubt, such tubers should not be planted, and specimens should be
Lmubmitted to the station for examination.
SThere are over 500 plants susceptible to the attacks of gallworms,
jnluding many. garden crops. It profits little to plant potatoes upon
S 132M0-19- 8

infested soil, this serving only to increase the number .4Jo i&Q
sites. If possible, a rotation should be practiced using "enoM
crops where such are suitable. The following susceptil *ii
to be avoided: .
,..~ "l. ":*.- i:.:.^ .

SUNSCALD, SUNBURN OF TUBERS. .: r
Under certain conditions of the weather the leaves of their
plant may become sunburned. This condition may result' w-:lii
sun comes out brightly after a period of cloudy or misty w- il
The tender leaves wilt and later become dry and brown. This i.A
ease has not been found of much consequence in Hawaiian O$is
Young plants frequently appear drooping in the middle of the..
if the sun is hot following showers, but little burning or petm i
injury to the plants has been observed. 4.3
When growing tubers become exposed to the action of the'si
light, they develop cholorophyll (leaf green) and are said WlbetIS
burned (locally called "moonstruck"). As a result of disdez '.iik.
Rhizoctonia root disease (p. 24), which cause the tubers to develbpiO
short stolons and in a bunch next to the stem, the tubers "r'eif.
quently forced out of the soil. '"'
Control.-Hilling up the plants and attention to the conttoIQ
such diseases will remedy the condition. ;"..
,~~ : '.. .. "v'. '
LEAF TIPBUBN. .......
The disease characterized by the drying up, dying, and rolldgi4l
ward of the tips and the margins of the leaves during ae pei:.ndM
.... :.: g
.... .. .

Protracted dry weather is called tipburn (PI. XV). The older, or
Lower, leaves are most affected. This trouble may possibly be mis-
| taken for early or late blight. The absence of definite spots with con-
centric markings distinguishes it from the former, while the dry and
Supward-curling leaf margins of tipburn should serve to differentiate
Sit from the late blight. Tipburn is most common on light soils
which lose moisture rapidly. The disease results from the fact that
under certain conditions the plant loses water faster by transpiration
evaporationn from the leaves) than its roots can absorb water.
Control.-Good surface cultivation to conserve the soil moisture
and spraying with Bordeaux mixture have been found valuable means
of -preventing tipburn.
HOLLOW POTATO, PRONGED POTATOES.
The peculiarity known as hollow potato or black heart occasionally
occurs in Hawaii. As the name indicates, the centers of the tubers
are hollow or blackened. This trouble is considered to be due to
peculiar conditions of growth. Uneven development, such as rapid
growth following a period of cessation of growth or slow growth dur-
ing drought, is thought to be a factor in the production of hollow
potato and is also thought to encourage the formation of prongy
potatoes. Large, overgrown tubers are more frequently hollow than
average sized tubers, and in mainland States certain varieties seem
to be more commonly affected than others.
ARSENICAL INJURY.
The application of Paris green to the leaves of the potato without
mixing with it any neutralizing agent such as lime often causes the
death of a portion of the leaf or of the entire leaf. Arsenate of lead
is much less active in this way and is to be preferred for use on the
foliage of plants. In a moist climate, basic arsenate of lead is prob-
ably the best form to be used. Powdered arsenate of lead might
well be substituted for Paris green in the flour poison bait used for
the cutworms and army worms (" poko") where the bait is dusted
over the foliage. If Paris green is used, an equal amount of slaked
lime should be added to prevent burning.
The application of arsenicals in spray form for pest control has
been until recently but little practiced in the islands. Either Paris
Green or arsenate of lead can be used with Bordeaux mixture with
Little possibility of injuring the foliage. If Paris green rather than
Sarsenate of lead is used, a small additional quantity of lime may be
'. added to the Bordeaux to neutralize the Paris green. When a water
| suspension of Paris green is used for spraying, an equal amount of
* quicklime should be slaked and added to the water.
Ii

35

have not yet become established in Hawaii. Anong.
have not yet been observed are the following para.iti...
Black wart (which is one of the most destructive di&eas :i
known), powdery scab, blackleg, southern bacterial wil4%,iJ
Verticillium wilt, and leak; and the following suppose*dli
sitic diseases of unknown causation: Internal, brown spolt...
sis, curly dwarf, leaf roll, and mosaic. Among the insects
to the potato not yet detected here are the Colorado pqati
*"v .. *i.: ,.!*":

FIG. 6.-A potato affected with potato wart. (From U. S. Dept. Agr., FVDUI
and species of flea beetles. The diseases above enumerated. r,
scribed in order that they may be recognized promptly and&i|
better guarded against.. It is quite possible that some. 0oif
eases are already present in the islands but have snot yet3
notice. In any cases where diseases are thought to- be i
hereinafter described, specimens should be forwarded without
to this station for determination. A .-.i.
PARASITIC DISEASES. '" ...
BLACK WABTr .(Chrysophlyctis endobiotir). ..T
The black wart disease was discovered upon potatoes.i n.
less than 25 years ago. Since its discovery it 11ha spred w4
rapidity in Europe and has recently appeared inNewfoufdl41
-T ~

....f. ..., POTATO DISEASES T HAWAII. 37
*ii.: I .::' "":.-:,E.. "N.= "..E.
.. tly been found in gardens in certain mining towns of
i, aid a survey of the infected region is now in progress.
w. rt is probably brought into new localities on apparently
hyor. only slightly diseased potatoes coming from infected
Sand it is thought to have been introduced into the United
We.ks6u low-grade European table potatoes before the quarantine
S* tblished.
wart attacks the tubers chiefly and causes malformation
Swarthy excresences, converting the tuber into a worthless minass
: .. .. :, :. :: ,'."
I 4.g 6). The warts have given rise to such names as warty disease,
Sbbok scab, canker, and cauliflower disease. Once infected, a soil
.V .i not be used for this crop again for many years, unless resistant
S:.variete) are found, as now seems possible. In the -Worst cases from
25 paSr cintrup to the entire crop is affected. The disease grows'
Swore each year potatoes are grown on infected soil, but so far as
I known no other crop is attacked.
C, The seriousness of this malady may be judged from the following
quotations:
;; A vigorouS effort should be made, if found in the United"States, to eradicate
I-the"trouble. All infected tubers should be boiled or burned, and no more
....ipotatoed should be planted on that field for eight years. Stock should not be
.:. alo'.d to ruin ovet infected areas anid no part of any lot containing diseased
potatoes should be used for seed purposes.1
S-:It- has been stated that no sound potato is saved from a crop that is
attacked. While the virulence of diseases like late blight or early blight is
More, or less dependent upon climatic conditions, this -disease -'is not influenced
in any knbwn degree by physical or mechanical conditions... It, may, there-
o foreb.e' -onidered as the htot serious pest attacking potatoes Fields at har-
vest ih affected areas present the most hopeless appearance; the disease has
Caused the greatest havoc in all localities where it has appeared.'
V
; POWDERY SCAB (Spongospora subterranean .
owder scab has only recently been introduced into the main-
IL4 of the United States, first being found in Maine and subse
quent!y in other New England States and more recently in Oregon
iAMd 'ashington, and it is also known to exist in British Columbia.
AtNNe disease, which may be mistaken for corky or common scab, is
caused by the slime mold Spongospora subterranean. There appears
-te. little indication that it would be serious if introduced here,
.,Iatfhologists of the Eastern States being of the opinion that its
" *. .".:.. ss- .:... .. -- ^ '^
sp; read will be largely controlled by climatic and soil factors. The
|fungus attacks the.. young tubers and develops as they mature in
te ground. The, center of infection becomes a pustular-like scab
%mining the spore balls of the fungus as a brown powder. The
4:) V..lgZEthel (. [Ilh WA. disease of the potato.] U. S. Dept. Agr., Farmers' Bul. 489
iAit); p. 23.
GI... Gsow, IL,.T. A serious potato disease occurring in Newfoundland. Canada Dept.
p .Bua. 63 (1909), p. 6.

H.:':u. .

spots are as a rule smaller than those of the corky orF ,..4H
are more regularly rounded, and are characteristclly .t
the uplifted and torn skin. A canker stage also oocurs ad
this stage that causes the greatest loss. This scab may"jiq
way to various storage rots. ,
Control.-Since this disease occurs in the coast States, io
tions of potatoes from these should be carefully inspected tot i
this disease, and all mnai
~- A. ptatoes to be used for seed sbmd
disinfected with corrosi*e
blacle i th mate solution as a prec
S measure. This solution w
wr. .....to be only partially eedfstbwrM
destroying powdery scab
carried by the seed, but it Ubeit
(:i.g.~ : ).Int tber aroo than formalin. Lots of poeta"B"
t s my containing suspicious tubers s i
r ... a,- por s dad epnot be planted, and pi.
.... ... e should be forwarded to the s
......... ,... .... -................
L losses.. of 50 pretfor examination. IW.:|B|
4 1. i:d 4 ." '
:'A ;t ... BLCx E (Bacl lus phYtOpkthf
., n '." ,... "" jfl :!"itz
a ..... Blackleg is a serious basoe.
A'# disease of the potato ccu. .rri* M ,j
the New England States, '

;R S.
Washington and Oregon, a'4#r {
sibly in California, but not A y
3E,:.; ..:. .. ..
observed in the Hawaiian Islamdai
t This is a disease of the stem sd
tuber, and, as its name suggests, .i...
lower part of the stem of dtwtbd
Fm. 7.-A potato plant affected wth plants becomes blackens4. ti..
blackleg in the summer stage, the result tubers themselves are destfo .....
of planting diseased tubers. The lower a soft rot. In the advancede'
part of the stem is shriveled and black, ..
the leaves are yellow and rolled up- the stem shows a black color,4
ward. (From U. S. Dept. Agr., Farm- extends from the seed if t
era' BEl. 544.)
some distance above theeg i
(fig. 7). In the tubers a rot often extends from the stolon, or elh IM
tubers may simply remain undeveloped. The use of infected: ...
results in a poor stand, and the plants become diseased.
In Europe the losses are reported at from 5 to 94 per cent, i
Maine the most common losses range from 1 to 5 per cent with .....
sional losses of 50 per cent. The damage is heaviest on low.,,
and poorly drained soils. '(WI 5,
.. "* i .: .
,. .. .. ,. ,'-"

i" ii.:"'
S: ::.. ::.* .
:" :. :: : ... ...

POTATO DISEASES IN HAWAII.

39

I- trol.-In Maine it is thought that the disease does not spread
friom hill to hill, and that it can be controlled there by seed selection
|; and disinfection. Here, where there is little change of season, it is
F conceivable that the disease might remain in the field from crop to
Scrop, and be much more serious. The porous, well-drained soils
would tend to minimize the damage should this disease be introduced.
T The liability of introducing this disease as well as others is added
S7:.:'evidence against the practice of using any imported seed except that
which is certified. The latter should be planted only after it has been
: examined and disinfected, as a small percentage of this disease is
S allowed in the growing fields, the product of which may later be
certified. "
SSOUTTHERN BACTERIAL WrrT (Bacillus solanattea4um),.-

This bacterial disease of the Irish potato is prevalent and destruc-
tive in the Atlantic States from Florida to New Jersey. Tomatoes,
S eggplant, peppers, and tobacco are also attacked. On tobacco the
disease is known as the Granville wilt. This malady is most destruc-
tive in dry seasons and on dry soils. The affected plants wilt,
S recover during the night, and wilt again the next day. Then they
S become yellowed or blackened, and the forming tubers are attacked
by a soft rot, which is accompanied by a very foul odor. Possibly
S this disease would be very destructive if introduced into the islands,
:. but considering the remoteness of the infected districts, there seems
little probability of this contingency.
Control.-Seed from uninfected fields should be selected and rota-
tion of crops practiced. Other solanaceous crops should be avoided
in the rotation. Insects should be controlled, as they are believed to
S carry the wilt from plant to plant.
SiLVEn ScuR (Spondylocladium atrovirens).
; This disease, probably recently introduced into the United States,
L is caused by the fungus Spondylocalaiwm atrovirer and is charac-
Sterized by a silvery appearance of the skin, with minute blackish
patches of the fungus thereon. It is not considered as especially
serious. The damage to the crop results from disfigurement, abnor-
mal shrinkage and shriveling of the tubers, and decreased market
S value of the product.
Control.-Seed selection and disinfection in corrosive sublimate
S are advised for the control of silver scurf.

*OJ I UjLn-il-i 1J %01 XIALWalXJl. j iVJaN 5.>;US : L*'"* ^ir^M ^
:4
The disease occurs in the Atlantic States and also.in the PacJeS ...
States. In general the Verticillium can not be considered. s' .iii'
as the Fusarium wilt, since only scattered plants in a-
attacked. Once a field is infected, however, the disase.:i
more serious from year to year if cultivation of susceptible! PH!-
continued.
Control.--The control measures suggested are the same as .
for the Fusarium wilt (p. 19). In the rotation the following sue *
tible plants must be avoided: Eggplant, tomato and other ..ohaiThii
ceous plants, okra, brambles, and cotton. *1i, S
.:' :;''... .^.',. l- lf.l
LEAK OR MELTES (Rhizopus nigricans and Pyth4um debaryatrum).., :...
X' i.
Leak or melters, the name applied to a rapid soft rot of tubirs'::,?
occurring in the delta lands of California, is a type of decay. oftn.0|
causing serious loss in shipments to markets. The disease wakts.-., .
first attributed to the common bread mold fungus Rhisopus Wmgr? a.ew,
but recent investigation has shown that it is in large part due to 'L
fungus Pythium debaryanum. These fungi enter through wounN
in the tubers made in digging. ,- i
Control.-Careful handling in digging and the sorting out of: af
bruised tubers previous to shipping has been found a practical B .me .,f
of control. P L-4.': i
NONPARASITIC DISEASES. ::..
." :. r :::
INTERNAL BROWN SPOT AND NET NECROSIS. ... :...,:."^
.. ..:- : A ,;flB
'* :..'... "* .. ..Jf
Brown spots and streaks in the flesh of the potato and more or lgs s
widesprQad net necrosis or netted brown streaks (vascular thre*d:sA.
occasionally occur under conditions of growth that are not' wel 'l
understood by pathologists. Dry weather and soils possibly deficient'
in some element of plant food are thought to be associated with' ,:-,
this trouble. As found on the mainland it is sometimes associa9M f
with temperature changes, probably both during the maturing paiot: :
and in storage. It is significant that neither internal brown 'mpli:';
nor net necrosis has been observed here, where a uniform tenm].pe.t ....,
ture is the rule. '"'
..tt.% I .
*~ "*: i w -i:' ^;'" T
.. t ';-.. :',
CuRLY DWARF, LEAF ROLL, AND MOSAIC. ..-:,;; "

The diseases known under the names curly dwarf, leaf roll,. uju.. t
mosaic are all imperfectly understood and the causes are entirely: 'X:
unknown at the present time. The first two are inherent troublS 'ia4)
which appear to be associated with weakened strains of potatoes., :-i V

1| ie growing of Irish potatoes in Hawaii, though an industry of
V: ehsiderable importance, has been largely discouraged in recent
i*ers by persistent crop failures and unfavorable marketing condi-
#ions. It is desirable that the islands become self-supporting so far
-tas possible with respect to this commodity. It is believed that the
potato crop can be doubled without any increase of acreage by the
Adoption of modern agricultural methods.
I Crop 'failures, which have been found to be a persistent source of
x, loss, are brought about by the following factors: (1) The use of poor
M..: seed, (2) continuous cropping (as many as three or four crops a year
fl with no systematic rotation for a half century or more), (3) diseases
.A and insect pests, and (4) unsatisfactory soil conditions. Fundamen-
s tally the diseases have been the most important factor, with the other
IHN4 mentioned factors as contributing causes.
SThe diseases, so far as they have come to the attention of the writer,
C::: i have been determined, and recommendations have been made for their
, control, both through the improvement of cultural practices and
Through special methods where required. Certain diseases which are
destructive in other localities but have not yet been found here are
0. described in order that their introduction may be the better guarded
. against.
The following diseases and pests of the Irish potato have been
Found to occur in Hawaii: Fusarium wilt (Fusarium oxysporum),
: late blight (Phytophthora infestans), early blight (Alternaria
|sottmi), black scurf and rosette (Rhizoctonia solani), Sclerotium
1 wilt (Sclerotium rolfsii), common or corky scab (Aotinomyces
Schromogenus), tuber rots (Phytophthorm infestans, Fusarium oxy-
a porum, F. radicicola, and F. coeruleunm), tuber moth (Phthorimaea
operculella), cutworms (and a similar leaf-eating worm locally called
S"poko"), mite disease (an unidentified form of Tetranychida),
Snematodes (Heterodera sp.); and the nonparasitic troubles sunscald,
Sunburn of tubers, leaf tipburn, hollow potato, pronged potatoes,
'.arsenical injury.
S The universal adoption of the practices of seed selection and dis-
infection, crop rotation, and spraying with Bordeaux mixture are
re:,::::zscommended for the general improvement of the potato situation.
.:. Only through the use of healthy, vigorous seed and fertile, disease-
fr ee soils, maintained through crop rotation, can healthy crops be
.secured. When once healthy plants, in other words, plants worth
Saving, are assured, the value of Bordeaux mixture in preventing
late blight, the most serious potato disease in Hawaii, will be more
Readily seen, and under improved cultural conditions spraying will

-/ -* -- V -. .5 .5.A : ?v ^i-|
some of the growers are taking up spraying and other" 'N.ip4 ..
ment measures with commendable zeal, and sprayed plants
increases of from 50 to 200 per cent over unsprayed plates.."?: ,
trolling the late blight, a locally developed variety appearst"o
considerable promise in resisting foliage injury. "
The improvement of the potato crops can be permanently brisl.
about only through a realization of the importance of the 6
factors involved in the crop failures, and especially the diseases
pests must be prevented. This can be accomplished only through 4t
use of good seed, fertile, disease-free soil, and spraying, combine
with the best cultural methods.